1. Field of the Invention
This invention covers the field of medicine, in particular, biochemistry and biomaterials extraction technology and is also used for manufacturing of biomaterials applied as a plastic material by the operative restoration of bone defects by destruction of bone tissue, cystectomy, oncotomy and also as a carrier of active substances and drugs, in plastic surgery by restoration of organ's or tissue's volume.
2. Description of the Related Art
A bone is a living tissue, in which a continuous reorganization process including a simultaneous destruction and restoration of the bone material. Old tissue is remodulated during a normal process and also by implantation of a foreign material, new tissue is formed in place of this. Equilibrium is permanently maintained between the quantity of a reformed bone and a newly developed bone. This process will go easier, if the implanted material is close to a natural bone in its structure.
That is why at present it is preferred to prepare the substitute material from tissues of a natural bone, which is normally of animal origin.
It is well-known that a partial demineralization promotes implantation of a bone graft. Hereupon various additional steps are taken, which are intended either for full deproteinization of the bone or for influence onto the nature of proteins remaining bound in the bone base or for increase of this share of proteins.
Methods used heretofore, in particular, U.S. Pat. No. 4,394,370 can be given as an example, where it is proposed to form a spongy mass by melting of a mixture consisting of a powder of the demineralized bone of human origin and a dilutes collagenic powder with the help of glutaraldehydic binding providing a cross-link.
U.S. Pat. No. 4,743,259 combines demineralization by the hydrochloric acid with enrichment by proteins carried out on the first part of the demineralized bone with the help of proteins extracted from the second part with use of guanidine.
Furthermore, FR No. 2,582,517 proposes to process bone ends taken from animals, namely, from livestock by means of a partial demineralization and tanning with use of glutaraldehyde. Bone fragments to be implanted by a surgeon are cut out with necessary shaping from cattle's bones after a preliminary pretreatment including delipidization or defatting operation with use of an organic solvent such as ethanol, demineralization with use of calcium extraction means such as hydrochloric acid and an operation providing for tanning with glutaraldehyde and also various washing operations.
It is obvious from description of patens given above that the mentioned tanning process favours to the features of a treated bone, as it facilitates the cross-linkage of macromolecular chains. However, it is recently detected that the treatment of glutaraldehydes does not result in a significant reduction of immunogenic features and, moreover, the engraftment of the implanted bone occurs in a desirable degree, as opposed to the theory suggested earlier. Furthermore, such chemical compounds like glutaraldehyde have a disadvantage—they are biologically toxic.
A method for obtaining of a material for osteoplasty from the bone issue of natural origin including the subsequent removal of lipids from the natural bone issue with use of an organic solution, selective extraction with the subsequent washing and lyophilization of the end product is known, characterized by that that the selective extraction is carried out with use of the urea solution for denaturation and removal of antigenic proteins with maintaining of a non-denaturated collagen of type I in a natural form located in the initial mineral bone structure and the obtained structure is directed to washing and lyophilization (RU Patent No. 2,104,703, publ. Feb. 20, 1998).
At that, the removal of lipids is carried out with use of the organic solution containing 10 volumetric parts of chloroform/methanol or ethanol/dichloromethane mixture per 1 part of bone in proportion of about 2:3-1:3 accordingly. The demineralization of the bone tissue is carried out with the solution of the hydrochloric acid with molarity of 0.1-1.0 M after removal of lipids. The extraction with an ionic solvent is carried out before the selective extraction, in particular, with use of sodium chloride.
The selective extraction is conducted with a 2-10 M urea solution, preferably with a 5-8 M solution or aqueous urea solution containing 0.1-0.5 vol. of mercaptoethanol. The washing is carried out with use of distilled water at 30-60° C., preferably at 45-55° C. Alternatively, the selective extraction is carried out first with use of the urea solution in concentration of 2 to 10 M, preferably 5-8 M, then, after washing,—with use of the aqueous urea solution containing mercaptoethanol in quantity of 0.1-0.5 vol. in the solution.
The material for osteoplasty obtained by such a way represents a compound, in which the bone structure of natural origin containing 20-40% (namely 25-35%) of a non-denaturated collagen of type I is maintained. According to analysis results of dry material, this material contains less than 15% lipids, 25-45% proteins, 10-30% calcium, 5-20% phosphorus and has the water content below 10% and Ca/P ratio in preference from 1 to 2.2.
The material can have a shape of parallelepipedic blocks, truncated pyramids, plates, discs or powder amalgamated with a binder which can be in preference of biological origin such as fibrin or synthetic origin such as, for example, synthetic biodegradable polymer.
This invention is chosen as a prototype both for the method and material, as it is the closest to the proposed invention as regards its engineering solution.
The disadvantage of the mentioned method is the fact that such treatment, although it maintains a bone collagen of type 1 in the natural form, does not provide full removal of antigens—non-collagenic proteins, lipids, lipoproteins and other substances reducing the biocompatibility of the obtained material from this tissue.